1. Field of the Invention
The present invention relates generally to an image forming apparatus comprising a redundancy system, and more particularly, to an image forming apparatus comprising a functional redundancy system as a redundancy system.
"Functional redundancy" means "using a part which originally exists in an apparatus and making use of the part utilizing a potential function of the part as a substitute for another part".
2. Background of the Invention
At the present time machine civilization advances, failures in an apparatus system exert very great effects on society. Accordingly, various types of maintenance have been performed on the apparatus system.
The following three means have been generally considered for the maintenance on the apparatus system. Specifically:
1. High-reliability design: making such design that no fault occurs in the apparatus system. PA1 2. Preventive maintenance: preventing a fault from occurring in the apparatus system during the use. PA1 3. Corrective maintenance: preventing, even if a fault occurs in the apparatus system, the fault from affecting the whole apparatus system to recover its function in a short period of time.
However, there are limitations of such concepts. First, as for the high-reliability design, there is a physical limitation of increase in quality of parts, and the cost of the apparatus system is liable to suddenly rise. In addition, in considering redundant design for ensuring the reliability, the sudden rise in cost due to the hugeness of the apparatus system cannot be ignored. Furthermore, in considering fault tolerant design or as for the preventive maintenance, the fault must be able to be expected. However, it is difficult to expect the fault as the apparatus system is complicated.
On the other hand, if the effect of the failures in the apparatus system on society is considered, it is actually very dangerous to consider only fail-safe and the corrective maintenance.
Therefore, it is necessary to positively recognize the possibility that a fault occurs and consider measures taken to prevent, even if a fault occurs, the fault from exerting a functional effect.